Diesel engine systems are utilizing Selective Catalytic Reduction systems (SCR) downstream of a Continuous Regeneration Trap (CRT) (also referred to as a Filter Trap), to limit or control emission of nitrogen oxides (NOx) into the atmosphere. Such Diesel engine systems have also been designed which include a CRT canister housing a Diesel Particulate Filter (DPF) and a Diesel Oxidation Catalyst (DOC) upstream of the DFP. Near the connection ends of the CRT, the upstream and downstream exhaust pipes are provided with inlet and outlet temperature sensors. The temperature sensors are used to determine when to inject diesel fuel to burn-off accumulated diesel soot on the DPF, commonly called dosing. A third temperature sensor controls the doser to prevent overheating and ultimate failure of the CRT.
An SCR downstream of the CRT may be used to further reduce NOx emissions. This SCR is similar in design to the DPF having a canister and temperature sensors located near the connection ends of the canister. Housed within the canister is an Ammonia Oxidation Catalyst (AOC). A gaseous reductant, typically aqueous ammonia or urea, is added to the exhaust gas stream and is absorbed onto a catalyst. Carbon dioxide (CO2) is a reaction product when urea is used as the reductant.
CRT's and SCR's are manufactured from various ceramic materials used as a carrier, such as titanium oxide, and active catalytic components are usually either oxides of base metals (such as vanadium, molybdenum and tungsten), zeolites or various precious metals. Both are expensive to replace and sometimes stolen for profit. This can be of great cost approaching $4000.00 per vehicle including downtime for the vehicle owner. Some owners attempt to increase engine horsepower by replacing the flow-restricting catalytic devices with a straight or so-called “test pipe”, similar to what was done to some automobiles in previous decades. Such devices can be used in place of either catalyst in combination with a new engine code to “trick” the engine. This can result in voiding an engine warranty when detected. Additionally, the EPA can impose substantial fines regarding this practice.
Engines frequently undergo transient or changing operating conditions, such as a speed or torque transient. A system or method which detects a missing catalytic device during such a transient operating condition is desired.